Zeolite catalysts of improved activity and para-selectivity

Abstract

A method is provided for treating modified ZSM-5 type zeolite catalysts with water vapor in order to enhance the aromatics conversion activity and/or the para-selective properties of such catalysts for the conversion of aromatic materials. The modified zeolites so treated are those which contain a minor proportion of a difficultly reducible oxide such as magnesium oxide, calcium oxide and/or phosphorus oxide. Such catalyst compositions can be used in alkylation, transalkylation or disproportionation processes to provide improved yields of alkylated aromatic product mixtures having exceptionally high concentrations of the para-dialkylbenzene isomer.

What is claimed is: 
     
       1. A method for treating a chemically modified zeolite catalyst in order to enhance the aromatics conversion activity and/or the para-selectivity of said catalyst, said catalyst comprising both a crystalline zeolite material having a constraint index within the approximate range of 1 to 2 and a silica/alumina mole ratio of at least 12 and a minor proportion of one or more difficultly reducible oxides selected from the group consisting of oxides of the metals of Groups IA, IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIIB, IVB and VB of the Periodic Chart and combination of phosphorus oxide with one or more of said metal oxides, said method comprising the steps of: (i) contacting an inert inorganic gaseous diluent with liquid water, whereby said diluent becomes essentially saturated with water in the vapor state, and whereby water in the liquid state becomes dispersed in said diluent;   (ii) converting essentially all of said liquid water dispersed in said diluent to water in the vapor state by increasing the temperature of the water-containing diluent of step (i) to a temperature sufficient to accomplish such conversion; and   (iii) contacting said catalyst with said essentially liquid water-free diluent of step (i) at a temperature between about 40° C. and 700° C. for a period of from about 1 to 72 hours and at a rate of at least about 0.005 gram of water per gram of catalyst per hour.   
     
     
       2. A method according to claim 1, whereby the increase in temperature achieved according to step (ii) is sufficient to at least double the vapor pressure of said water. 
     
     
       3. A method according to claim 1, wherein said inorganic diluent is selected from the group consisting of air, nitrogen, carbon dioxide, helium and mixtures thereof. 
     
     
       4. A method according to claim 3, wherein said contacting step (i) takes place at essentially ambient temperature, and wherein the temperature of said water-containing diluent of step (i) is increased to a temperature between about 40° C. and 700° C. in step (ii). 
     
     
       5. A method according to claim 4, wherein said steps (ii) and (iii) take place by maintaining said catalyst in a heated reactor and by passing said water-containing diluent of step (i) into said reactor. 
     
     
       6. A method according to claim 1, wherein said difficultly reducible oxide is selected from magnesium oxide, calcium oxide, combinations of magnesium oxide and phosphorus oxide and combinations of calcium oxide and phosphorus oxide. 
     
     
       7. A method according to claim 1, wherein the temperature of said water-containing diluent of step (i) is increased to a temperature from about 50° C. to 500° C. in step (ii). 
     
     
       8. A method according to claim 4, wherein said diluent is air. 
     
     
       9. A method according to claim 1, wherein said zeolite is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48. 
     
     
       10. A method according to claim 1, wherein said catalyst comprises only one difficultly reducible oxide, which is magnesium oxide, said catalyst not comprising phosphorus oxide. 
     
     
       11. A method for treating ZSM-5, said ZSM-5 comprising a minor proportion of one or more difficultly reducible oxides selected from the group consisting of oxides of the metals of Groups IA, IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIIB, IVB and VB of the Periodic Chart and combinations of phosphorus oxide with one or more of said metal oxides, said method comprising the steps of: (i) moistening air with water at ambient temperature; and   (ii) passing said water moistened air of step (i) into a reactor containing said ZSM-5, said reactor being maintained at a temperature between about 40° C. and 700° C., for a period of from about 1 to 72 hours and at a rate of at least about 0.005 gram of water per gram of catalyst per hour, whereby said ZSM-5 is contacted with water vapor.   
     
     
       12. A method according to claim 11, wherein said catalyst comprises only one difficultly reducible oxide, which is magnsium oxide, said catalyst not comprising phosphorus oxide.